The occurrence of _Myeloxylon_ petioles in the New World was recorded by the late Prof. Penhallow[288] who founded this species on some imperfectly petrified specimens from Upper Carboniferous strata at Topeka, Kansas. Enough material was available to show the _Myeloxylon_ characters, but the preservation is too imperfect to admit of a complete diagnosis. The hypodermal stereome shows a tendency to form tangentially extended strands in place of the more circular or radially elongated groups in the European species. In addition to _Alethopteris_, _Neuropteris_ (including _Cyclopteris_) and _Odontopteris_ fronds, which are known to possess rachises with the _Myeloxylon_ features, there is reason to believe that the Permian _Callipteris_ fronds and possibly some of the older _Taeniopteris_ leaves may also belong to _Medullosa_[289]. It is, however, unsafe to assume that the occurrence of _Myeloxylon_ petioles necessarily denotes the existence of _Medullosa_. The French stem _Colpoxylon aeduense_ Brongn.[290] bore leaves with the same general anatomical features as those of a typical _Myeloxylon_, and there can be little doubt that other genera of the Medulloseae also possessed fronds constructed on the same plan as those known to have been borne by _Medullosa_. An interesting illustration of an injured organ that had produced a wound-cambium is afforded by a _Myeloxylon_ petiole from the Coal Measures described by Mr Holden[291]. +Reproductive Organs.+ Reference was made in volume +ii.+ to the reasons which led to the removal of several genera of Carboniferous and Permian fronds from the Filicales to the Pteridosperms, and in Chapter +xxix.+ of the present volume certain species of _Sphenopteris_ are described as the foliage of _Lyginopteris_ and _Heterangium_. It is with such genera as _Neuropteris_, _Alethopteris_, _Linopteris_ and others that we are now more especially concerned, as they represent some of the types of leaves borne by _Medullosa_ and other members of the Medulloseae. The absence of any specimens among the large number of these common genera bearing undoubted sporangia aroused suspicion as to the correctness of the generally accepted view that these fern-like fossils were the leaves of Palaeozoic Ferns. Subsequently the suspicion based on negative evidence was confirmed by researches into the anatomical structure of the leaf-bases, petioles, and fragments of pinnae attached to and associated with stems of _Medullosa_. It is only in a few cases that actual organic connexion between reproductive organs and Medullosan leaves has been demonstrated, but from such facts as are established it is safe to make the general statement that stems of _Medullosa_—a generic term that undoubtedly includes plants which, had we a fuller knowledge of them as complete individuals, would be assigned to more than one generic type—possessed fronds simulating in habit those of certain Ferns with some of the pinnae bearing seeds